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酸碱改性负磁生物炭对四环素的去除机理分析
湖南农业大学 何洋州,何阳卓,刘晓成,徐彬湖南农业大学资源环境学院&国际学院环境科学系,湖南 长沙 410128
(已与导师共一发表并在论文致谢中标注大学生创新训练项目资助及国家级项目号,期刊:Science of the Total Environment, 2019, 650: 2260-2266)
指导教师:周耀渝教授,罗琳教授中文摘要:四环素作为一种广泛使用的抗生素,对人体健康带来了巨大的隐患。城市污泥作为一种富
含有机物的生物质用以生产生物炭具有潜在应用价值。在这项工作中,采用酸碱结合法对作为固体废弃物的污泥类生物炭进行改性,从而有效地去除水溶液中的四环素。在四环素初始反应浓度为 200 mg/L 下最终去除效率可达到 86%,在去除机理探究方面,通过测定活化能,研究不同温度和四环素浓度下的吸附动力学可以得出,四环素与改性生物炭在反应中主要为吸热反应。同时提出朗缪尔 -弗伦德利希模型,通过计算生物炭位点的能量分布,并重点推导四环素在改性生物炭上的平均位点能量和相应的位点能量分布标准差,以获知四环素在改性生物炭上的吸附强度和位点的异质性。研究方法证明改性污泥生物炭去除污染水中的四环素具有很大潜力,并通过量化平均位点能量探索四环素的去除机理,从而可将研究成果和方法延伸用于水处理系统的研究中。
英文摘要:As a widely used antibiotic, tetracycline has a huge hidden danger to human health. Municipal
sludge rich in organic substances has the potential to produce biochar. In this work, the municipal sludge biochar
from solid waste was modified by the alkali-acid binding method, and tetracycline was efficiently removed from
the aqueous solution, the adsorption removal efficiency reached to 86% at initial concentration of 200 mg/L. The
activation energy was determined by analyzing the adsorption kinetics at different temperatures and tetracycline
concentrations. The results showed that tetracycline adsorption on modified biochar was endothermic reaction.
Presenting the Langmuir-Freundlich model, adsorption site energy distributions was reckoned. The average
adsorption site energy and corresponding standard deviation of the adsorption site energy distribution were
deduced emphatically to inquiry the strength of tetracycline adsorption on modified biochar and the adsorption site
heterogeneity. The method proposed of research further proves that modified biochar from sewage sludge remove
tetracycline from contaminated water has great potential, and exploration of tetracycline adsorption mechanisms
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by quantifying average site energy. The results and methods of this work can be transferred to study water
treatment systems.
关键词:四环素;改性生物炭;城市污泥;吸附模型;位点能量分布。
Analyses of tetracycline adsorption on alkali-acid modified magnetic
biochar: site energy distribution considerationYaoyu Zhoua*1, Yangzhou Hea,1, Yangzhuo Hea, Xiaocheng Liua, Bin Xua, Jiangfang
Yub, Chunhao Daia*, Anqi Huanga, Ya Pangc, Lin Luoa
a College of Resources and Environment, Hunan Agricultural University, Changsha
410128, China;
b College of Environmental Science and Engineering, Hunan University, Changsha
410082;
c Department of Biology and Environmental Engineering, Changsha College,
Changsha 410003, Hunan, China.
*Corresponding Author at College of Resources and Environment, Hunan Agricultural University,
Changsha 410128, China. Email: [email protected]; [email protected] (Y.Y. Zhou),
[email protected] (C.H. Dai), 1 Yangzhou He and Yaoyu Zhou contributed equally to
this work.
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Graphic Abstract
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Abstract
As a widely used antibiotic, tetracycline has a huge hidden danger to human health.
Municipal sludge rich in organic substances has the potential to produce biochar. In
this work, the municipal sludge biochar from solid waste was modified by the alkali-
acid binding method, and tetracycline was efficiently removed from the aqueous
solution, the adsorption removal efficiency reached to 86% at initial concentration of
200 mg/L. The activation energy was determined by analyzing the adsorption kinetics
at different temperatures and tetracycline concentrations. The results showed that
tetracycline adsorption on modified biochar was endothermic reaction. Presenting the
Langmuir-Freundlich model, adsorption site energy distributions was reckoned. The
average adsorption site energy and corresponding standard deviation of the adsorption
site energy distribution were deduced emphatically to inquiry the strength of
tetracycline adsorption on modified biochar and the adsorption site heterogeneity. The
method proposed of research further proves that modified biochar from sewage sludge
remove tetracycline from contaminated water has great potential, and exploration of
tetracycline adsorption mechanisms by quantifying average site energy. The results
and methods of this work can be transferred to study water treatment systems.
Keywords: tetracycline; modified biochar; adsorption sites; adsorption modelling; site
energy distribution.
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1. Introduction
Antibiotics are emerging pollutants widely applied in animal husbandry and human
medicine, receive much emphasis of research (Chen et al., 2017; Liu et al., 2017a;
Norvill et al., 2017). Tetracycline (TC) is a commonly used antibiotic in cultivation
and livestock husbandry. Due to soil infiltration and incomplete animal metabolism,
most parent compounds are released into the aquatic environment in their original and
metabolic form (Conde-Cid et al., 2018; Zhu et al., 2014). Researchers analyzed the
concentration of TC in rivers affected by livestock life in Chengmen Rivers, Kam Tin
and in Yuen Long Hong Kong, and found that TC concentrations ranged from 30 to
497 ng/L (Selvam et al., 2017). In addition, antibiotics such as TC will induce to the
produce antibiotic resistance genes (ARG) in the microorganisms (Li et al., 2017;
Wang et al., 2016). It can be widely spread in the ecological environment and poses a
major risk to human health (Huang et al., 2016).
At present, there are various technologies for eliminating TC such as adsorption,
chemical, photolysis, biodegradation and electrochemical oxidation (Liu et al., 2017b;
Liu et al., 2017c; Liu et al., 2018; Strasse, 2009; Zhao et al., 2017). Among these,
adsorption is widely recognized as a large-scale and cost-effective method (Zhou et
al., 2017c). However, for adsorption applications, it is still necessary to seek an
economic, efficient, green, sustainable and easily separated adsorbent. Biochar is the
carbon-rich solid that produced through the pyrolysis of biomass in anoxic
environments (Shen et al., 2017; Wu et al., 2017). It has multi-empty structure and
relatively abundant functional groups, (Liu et al., 2015), which is entrusted with
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adsorption performance.
Municipal sludge (MS) is a major by-product of municipal wastewater treatment
facilities, considered solid waste contaminant. It is rich in organic matter that allows
MS to have the potential to produce biochar (MS-biochar). However, the adsorption
performance after single modification of MS-biochar is not satisfactory (Tang et al.,
2017). Recently, based on the corresponding components of urban sludge, our
previous studies have shown that TC can be effectively adsorbed by alkali-acid (AA)
binding method modified MS-biochar (AAMS-biochar) and determine the optimal
solution pH for TC adsorption is 7.0 (Tang et al., 2017). Comparing other adsorbents
such as goethite adsorbents (1.92 mg/g) (Zhao et al., 2014), bamboo charcoal
adsorbents (22.7 mg/g) (Liao et al., 2013), iron-montmorillonite adsorbents (37.21
mg/g) (Wu et al., 2016), and graphene oxide adsorbents (39.1 mg/g) (Lin et al., 2013),
AAMS-biochar shows higher adsorption capacity for TC (286.913 mg/g at pH 7.0)
(Tang et al., 2017). In addition, the magnetic properties of the AAMS-biochar itself
can be effectively magnetically separated and recovered. Therefore, AAMS-biochar
has good regeneration performance, the performance after five cycles decreased
slightly (Tang et al., 2017). However, with respect to the kinetics of TC adsorption
processes, systematic studies of temperature characteristics such as isotherms and
adsorption energy have not yet been completed. It is crucial for research the
mechanism of TC and AAMS-biochar adsorption and related application in the
treatment of water contaminated with TCs and the like.
In the adsorption of sorbates from benzene rings, it has been proposed that the
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interaction of π-π electron-donor-receptor (EDA) is one of the main driving forces
(Liao et al., 2013; Lin et al., 2013). The tetraphenyl ring structure is contained in the
molecular structure of TC, the π-electron-acceptor is considered to the benzene ring of
TC (Lin et al., 2013), while the π-electron-donors is aromatic groups on
heterogeneous adsorbents (Liao et al., 2013; Liu et al., 2012). It remains to be further
studied the effect of the π-π electron-donor-receptor interaction on TC adsorption.
Moreover, it is helpful to understand the adsorption mechanism of the target molecule
by analyzing the adsorption site energy distribution. The energy intensity of binding
sites for TC adsorbed on the adsorbent is obtained from the curve of site energy
distribution, which helps to elucidate the adsorption mechanism (Jin et al., 2016;
Kumar et al., 2011). However, analysis of the effect of temperature on the energy of
TC adsorption sites has not been completed.
Herein, in this work, the isotherms and adsorption kinetics involved in the TC
adsorption on AAMS-biochar were studied at initial TC concentrations and different
solution temperatures. The adsorption site energy distribution was determined by
simulating the equilibrium TC adsorption data, and the interaction between the
adsorbent and the energy non-uniformity at the adsorption site were analyzed.
2. Materials and methods
2.1 Materials preparation
The used materials and chemicals were presented in supporting information. The
reported strategies (Tang et al., 2017). Typically, municipal sewage sludge was sieved
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through the 100 mesh sieve (0.15 mm) after drying and put into tube furnace (SK-
G04123K, China) at a heating rate of 5 °C/min under nitrogen protection, calcining
for 2 hours. MS-biochar was obtained from an optimum pyrolysis temperature of 800
°C. First stir with sodium hydroxide (2 M) in a 90 °C water bath for 2 hours, then
soaked with concentrated nitric acid (14 M) at 10-15 °C, with magnetic stirring.
The structural information of SEM (Zeiss Merlin), the magnetic property, Fourier-
transform infrared spectrum (FT-IR), and porosity and surface area of AAMS-biochar
were described in our previous work (Tang et al., 2017). It showed that AAMS-
biochar was rich in oxygen-containing functional groups and its average pores, pore
volume and surface area were enhanced. The oxygen-containing functional group on
the outside of the AAMS-biochar and the increased average pores, pore volume and
surface area mean that they contain both hydrophilic and hydrophobic sites.
2.2 Batch experiments
For the batch adsorption studies, with the optimal pH value (pH 7.0), each sample
contained 20 mg adsorbent and 20 mL TC solution at 298, 308, 318 K which shaking
at 160 rpm. In the kinetic experiments, obtaining the kinetic data at 5, 10, 20, 30, 60,
120, 180, 300, 420, 600, 840, 960, 1080, 1200, 1320, and 1440 min with 200 mL
initial TC concentration. In the adsorption site energy distribution analysis
experiments, the initial concentrations of TC ranged from 50 to 800 mg/L, the TC
solution temperatures were 298, 308 and 318 K, respectively. All samples were
filtered with a 0.45 μm filter which was proved to have no intercepting effects for the
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TC molecule, and then analyzed by a UV-VIS absorbance at 357 nm, and calculated
the standard deviation of the sample mean. All of the experiments were performed in
triplicates.
2.3. Experimental data modeling
Kinetics Analysis. The relationship between adsorption capacity and the number of
active sites on the adsorbent was used the pseudo-second-order kinetics model to
simulate (Zhou et al., 2017a). The pseudo-second-order kinetic model fitted well the
adsorption of TC on modified biochar derived from sawdust (Zhou et al., 2017b).
Adsorption of TC on AAMS-biochar will be simulated using this model in this work.
The rate constant indicates k (g/(mgh)), basic function equation is
(1)
at t = 0, integral with initial value qt = 0 gives
(2)
where qe is amount adsorbed of the adsorbate at equilibrium (mg/g), the effect of
different temperatures can determine the rate constant by analyzing the adsorption
kinetic data. By plotting the association of lnk and 1/T, the activation energy can be
determined, corresponding the Arrhenius equation (Eq. (3)) as follows,
(3)
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where R is universal gas constant of 8.314 J/(molK) and Ea is adsorption activation
energy (kJ/mol). The size of activation energy is one of a standard that distinguishes
between physical adsorption and chemical adsorption. Since the physical adsorption is
easily reversed, the balance can be quickly reached, so the energy requirement is
small. In physisorption, the activation energy usually does not exceed 4.2 kJ/mol.
Chemisorption is special, it involves more powerful forces, so chemisorption requires
more activation energy (Unuabonah et al., 2007; Ziegler, 1971).
Isotherm Model. Taking into account the various components of AAMS-biochar,
simulate experimental data with the Langmuir-Freundlich model (Sips, 1950) as
follows,
(4)
where qm indicates maximum adsorption capacity (mg/g); Ce represented the
equilibrium concentration (mg/L); possible excitation related to the binding energy is
(L/mg). And the adsorbent surface site inhomogeneity is .
Site Energy Distribution. Based on the relationship between equilibrium
adsorption capacity and adsorption site energy distribution, the interconnectedness of
the heterogeneous surface theory can be expressed below (Carter et al., 1995; Shen et
al., 2015),
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(5)
where qe(Ce) is the maximum adsorption of solute to the adsorbent, instead
of the local adsorption isotherm, and F(E) is the site energy frequency distribution
over a range of sites with homogeneous energies. Adsorption energy E denotes given
adsorption site of adsorption energy divergence between solvent (water) and the
solute (TC). It is generally assumed that integral range of the adsorption energy from
zero to infinity (Jaroniec, 1975).
For the Cerofolini approximation (Cerofolini, 1974; Seidel and Carl, 1989), the
correlation among equilibrium concentration (Ce), the maximum solubility of the
solute (Cs), maximum solubility of adsorbate indicates Cs, and adsorption energy (E)
as follows,
_^D_Dd__________ ॑ԷϨϨ____________
at 298 K, the Cs value of TC is 26 mg/mL in water, and that were speculative to be 69
mg/mL and 107 mg/mL at 308 K and 318 K, respectively (Cerofolini, 1974; Varanda
et al., 2006), by the method from references.
(7)
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where Es is adsorption energy when Cs = Ce (Seidel and Carl, 1989), according to the
reference point Es, E indicates to the divergence of adsorption energies between the
surface of the adsorbent in the solvent and the adsorbate. E can be determined by
substituting the Ce and Cs into Eq. (6). Incorporating Eq. (4) and Eq. (6), the
Langmuir-Freundlich isotherm model expressed as qe (E*) below,
(8)
where qe(E*) is then differentiated with respect to E*, and the distribution function
F(E*) of the approximation and adsorption site energies is obtained as follows
(Keiluweit and Kleber, 2009; Unuabonah et al., 2007),
(9)
Based on Langmuir-Freundlich model parameters, defining the site energy
distribution of AAMS-biochar on TC adsorption by Eq. (9). Due to uneven
distribution of energy produced, the maximum adsorption capacity qm is considered as
the distribution area:
(10)
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2.4. Statistical analyses
Modeling of kinetics analysis, isotherm data and site energy distribution was
conducted with Originpro 8.6 using user-defined functions to calculated and measured
values. And we also calculated the heterogeneity of the adsorption site energy on the
surface of AAMS-biochar.
3. Results and discussion
3.1 The sole systems for TC
The effect of contact time on TC uptake by AAMS-biochar with respect to
temperature was presented in Figure 1a. The rapid adsorption of TC recorded in the
first 6 hours, after which the adsorption rate slows until it reaches equilibrium. It can
be seen that the equilibrium adsorption capacity and the adsorption rate of TC were
increasing at a higher temperature.
Simulation results of TC adsorption at different temperatures based on pseudo
second-order model was illustrated in Figure 1b. The corresponding values for the
fitting results were listed in Table 1. This model fits well the data of TC adsorption
kinetics (R2 >0.999). In addition, 35.02 mg/(g·h) was the initial rate (calculated from
kqe2) of TC adsorption on AAMS-biochar (200 mg/L, 298 K and pH 7.0). This could
be caused by the good pore structure of AAMS-biochar and the modified functional
groups (Tang et al., 2017). Furthermore, as the solution temperature raised from 298
K to 308 K and 318 K, the initial rate of TC adsorption increased from 35.02 mg/(g·h)
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to 64.50 mg/(g·h) and 103.58 mg/(g·h). Adsorption kinetics might be affected by
temperature in two ways: 1) with the increase of temperature, the escalate of
equilibrium adsorption capacity qe was the enhancement of adsorption driving force
(qe − qt); 2) with increase of temperature, the rate constant k also mounted. The
Arrhenius equation could be used to quantify the adsorption rate constant k affected
by temperature.
“Inset Figure 1 Here”
“Inset Table 1 Here”
The pseudo-second-order kinetics model determined rate constant k at different
temperatures, Table 1 listed the corresponding values. The activation energy was
determined by substituting the rate constant k into the Arrhenius linear equation,
which was 19.90 kJ/mol. Because in physisorption, the activation energy usually does
not exceed 4.2 kJ/mol. Exceeding the value indicates that AAMS-biochar adsorption
TC was mainly through chemical adsorption (Unuabonah et al., 2007; Ziegler, 1971).
It was generally, the interaction of π-π electron-donor-acceptor and the hydrogen
bonding between the oxygen-containing groups on the surface of the AAMS-biochar
and the hydroxyl groups in the TC molecule were the cause of the rapid adsorption of
TC. In our previous work, FTIR spectroscopy showed that AAMS-biochar was rich in
oxygen-containing functional groups (Tang et al., 2017). Multiple groups in the TC
molecule (e.g., phenol, amino, alcohol, and ketone) may interact specifically with the
corresponding structure of biochar surface, and modifying biochar surface to enhance
their interaction (Ji et al., 2009). The π-electron-rich structures of AAMS-biochar and
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the amino functional group on TC also could occur Cation-π bonding (Ji et al., 2009).
In addition, several groups contained in the TC could serve as H-receptors or H-
donors (hydroxyl, amide carbonyl and amino), or as H-receptors (hydroxyl and
carbonyl) (Yang et al., 2016), which could form hydrogen bonds on the AAMS-
biochar.
3.2 Adsorption site energy distribution analysis
By determining the adsorption isotherms of TC for AAMS-biochar at temperatures
of 298, 308 and 318 K to obtain the energy of the adsorption site and illustrated in
Figure 2. With increase of temperature, the equilibrium TC adsorption capacity of
AAMS-biochar increased accordingly. The results reveal that TC adsorption on
AAMS-biochar was an endothermic reaction, and it was the same as the adsorption
process of TC on carbon nanotubes (Zhang et al., 2011). The Langmuir-Freundlich
model (Eq. (4)) was well fitted the adsorption process of TC on AAMS-biochar with
high R2 values, and the results were presented in Table 2. The similar n values
obtained at distinct temperatures indicate that the surface heterogeneity was similar
within the tested temperature range.
“Inset Figure 2 Here”
“Inset Table 2 Here”
Determination of site energy E* based on isotherm modeling and Eq. (6). Figure 3a
shows equilibrium TC adsorption capacity at distinct temperatures. With the increase
of TC adsorption on AAMS-biochar, the E* value decreased. This indicates that TC
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was preferentially adsorbed to the high-energy adsorbed sites, followed by low-
energy adsorbed sites. The energy distribution of the sites of TC adsorption for qm,
and at different temperatures on AAMS-biochar determined on the basis of the
Langmuir-Freundlich model (Eq. (9)) was shown in Figure 3b.
To understand the surface energy heterogeneity and adsorption affinity of AAMS-
biochar at different temperatures, the site energy was exploited as describing the
interaction forces between TC and AAMS-biochar. The width of the site energy
distribution was able to interpret the surface energy inhomogeneity of AAMS-biochar
(Keiluweit and Kleber, 2009). In order to obtain the average site energies (E*) of TC
adsorption on AAMS-biochar, the weighted mean was calculated as follows:
(11)
the weighted mean could be obtained by merging Eq. (9), Eq. (10) and Eq. (11),
(^() )(∫_^()▒〖 ^()(^ )^ 〗 )/(∫_^()▒〖 (^ )^
〗)_
In general, there was a positive correlation between adsorption affinity and average
site energy (Keiluweit and Kleber, 2009). Obtaining adsorption sites energy by
calculating Eq. (12), at 298, 308 and 318 K corresponds to 15.05, 18.51 and 22.51
kJ/mol, separately. The effect of solution temperature on the average site energy of
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AAMS-biochar was able to explain as follows. EDA interactions were the main
process of TC adsorption on AAMS-biochar. This was the attraction between
electron-deficient (acceptors) and electron-rich (donors), which was a polar
interaction (Foster and Fyfe, 1966). In this work, the π-acceptors was considered as
electron-deficient π-system (TC) and the π-donor was serving as electron-rich
aromatic π-system (AAMS-biochar) in the TC adsorption on AAMS-biochar.
Normally, the increase in the polarizability of the compound and related structure
would increase the intensity of π-electron donors and π-receptors. Static dipole
polarizability also increases with temperature (Adam et al., 2013; Blundell et al.,
2000), which made adsorbate (TC) and the adsorbent (AAMS-biochar) to be more
active π-acceptors and π-donors, enhancing the affinity of adsorption. It reflected that
the average site energy increases slightly with increasing temperature.
“Inset Figure 3 Here”
The site energy distribution illustrated in Figure 3b, characterize site energy
heterogeneity based on standard deviation e of site energy distribution. The standard
deviation e of site energy distribution was able to describe the adsorption site energy
inhomogeneity (Shen et al., 2015), which could quantify as follows:
(13)
merging Eq. (9), Eq. (10) and Eq. (11) give
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〖〗_^√((^() )〖^〗^ )D_Dd__
thus, calculating the standard deviation,
(15)
From Eq. (15), it can be seen that the values of AAMS-biochar at 298, 308 and 318
K were respectively 6.32, 6.35 and 6.39 kJ/mol. In general, the inhomogeneity of
adsorption sites originates from the defect structure of carbon-containing adsorbents
and the various carbon structures cross-linking and disordered arrangement. The
heterogeneous adsorption of graphitized carbon to organic contaminants was
attributed to these aspects (Mcdermott and Mccreery, 1994; Mcdermott et al., 1993;
Milewska-Duda and Duda, 1997). In addition, the adsorption sites heterogeneity may
also due to grafting functional group (Jing et al., 2014). In this study, AAMS-biochar
was obtained from alkali acid combined modified municipal sewage sludge biochar
induced functional groups and specific structure, e.g., hydroxyl and carboxyl groups,
caused to the heterogeneity of AAMS-biochar. The values of were similar, and at
the three testing temperatures, the values of e were close. It was indicating that the
surface heterogeneity of AAMS-biochar adsorbed TC was similar within the tested
temperature range.
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4. Conclusion
In summary, it is concluded that the main mechanism of TC on AAMS-biochar was
chemical adsorption, among which EDA interaction played an important role. As the
critical influence factor, the effect of temperature on the adsorption process were
summarized as follows: 1) as the temperature increased, the adsorption rate constant
increased, so that adsorption rate of TC increased; 2) at the higher temperature, more
binding sites activated, which increased the ability of AAMS-biochar to adsorb TC; 3)
the increasing in temperature enhanced the intensity of the electron acceptor and
electron donor and also enhanced polarizability of the static dipole, thus enhanced the
EDA interaction between AAMS-biochar and TC; 4) the increasing in temperature
made the electron density more uniform on the surface of the adsorbent, and thereby
reduced dispersion of EDA interactions of AAMS-biochar adsorbed TC. This
indicated that over the experimental temperature range (298 K-318 K), the
temperature increased, the energy inhomogeneity decreased.
Supplementary material
Supplementary section associated with this article can be found in the support information.
Acknowledgements
Y.Z. He and Y.Y. Zhou contributed equally to this work. This study was financially
supported by the National Natural Science Foundation of China (Grant No.
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51709103), the Natural Science Foundation of Hunan Province, China (Grant No.
2018JJ3242), China Postdoctoral Science Foundation (Grant No. 2018M630901),
National Students’ platform for innovation and entrepreneurship training program
support project of China (Grant No. 201710537015).
Nomenclature
the so-called frequency factor or pre-exponential factor
initial adsorbate concentration (mg/L)
equilibrium adsorbate concentration (mg/L)
maximum solubility of adsorbate in water (mg/L)
^__________________________________________________________
_ↀ_ↂ_ↄ_ↈ_⑄_⑆_⑈_⒔_⒖_⒘_ⓤ_ⓦ_ⓨ_┴_┶_┸_▄_坏ꆥ熊詭偔㞊訳_________ᘆɨ 鵁_̰
$ᘀ᭨锰䈀 䩃ܪ
difference of adsorption energy at and (kJ/mol)
value of the adsorption energy corresponding to = (kJ/mol)
site energy frequency distribution over a range of energies (dimensionless)
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site energy distribution over a range of energies (mgmol/(gkJ))
rate constant of the pseudo-second-order kinetic model (g/(mgh))
indicator of the surface site heterogeneity of the adsorbent (dimensionless)
adsorption equilibrium constant (L/mg)
experimental equilibrium adsorption capacity (mg/g)
equilibrium adsorption capacity obtained from kinetic model (mg/g)
energetically homogeneous isotherm (mol2/(gkJ))
maximum adsorption capacity (mg/g)
amount of adsorption at time t (mg g)
gas constant (8.314 J/(molK))
coefficient of determination
residual sum of squares ((mg/g)2)
temperature (K)
energetical heterogeneity (kJ/mol)
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average site energy (kJ/mol)
References
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Figure. 1. Kinetics analysis of TC adsorption on AAMS-biochar at various
temperatures, a) situation of contact time on TC adsorption on AAMS-biochar; b) 27
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pseudo-second-order equation fitting of TC adsorption on AAMS-biochar; c) the
activation energy of TC adsorption on AAMS-biochar. 20 mL TC solution, 20 mg
AAMS-biochar and pH 7.0. Note: TC: tetracycline, AAMS-biochar: Alkali-acid (AA)
binding method modified municipal sludge (MS)-biochar, Vertical bars correspond to
statistical standard errors, and data are the mean values ± standard errors of 3 samples
(n=3).
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Figure. 2. Adsorption isotherms of TC on AAMS-biochar at different temperatures.
Note: TC: tetracycline, AAMS-biochar: Alkali-acid (AA) binding method modified
municipal sludge (MS)-biochar, Vertical bars correspond to statistical standard errors,
and data are the mean values ± standard errors of 3 samples (n=3).
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Figure. 3. Site energy and corresponding distribution of TC adsorption on AAMS-
biochar at different temperatures, a) site energy E* on TC loading; b) site energy
distribution. Note: TC: tetracycline, AAMS-biochar: Alkali-acid (AA) binding
method modified municipal sludge (MS)-biochar, experiments were performed three
times (n=3), and data represent mean values of a representative experiment.
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Table 1
Kinetics Parameters for the Adsorption ofTC on AAMS-biochar.
Experimental Pseudo-secong-order
T(K
)
C0
(mg/L)
qe
(mg/g)
qe,cal
(mg/g)
k
(g/(mg ×h)
kq2e,cal
mg/(g·h)R2
RSS
(mg/g)2
298 200 121.80 ± 6.42 120.00 ± 7.06 (2.432 ± 0.206) 103 35.02 0.999 0.208
308 200 142.90 ± 4.67 141.82 ± 5.46 (3.207 ± 0.308) 103 64.50 0.999 0.157
318 200 159.26 ± 5.73 160.35 ± 4.39 (4.028 ± 0.487) 103 103.58 0.999 0.209
Note: RSS: residual sum of squares ((mg/g) 2), k•q2e, cal : initial rate of TC adsorption
on AAMS-biochar, mg/(g·h), TC: tetracycline, AAMS-biochar: Alkali-acid (AA)
binding method modified municipal sludge (MS)-biochar, data represent the means ±
standard errors of the means.
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Table 2
Fitting Results of the Langmuir-Freundlich Model for TC Adsorption on AAMS-
biochar.
T(K)qm
mg/g
(L/mg)
R2
RSS
(mg/g)2
298 224 ± 2.03 0.056 0.694 0.978 37
308 277 ± 5.59 0.058 0.725 0.982 112
318 293 ± 4.61 0.071 0.748 0.987 52
Note: RSS: residual sum of squares ((mg/g) 2), TC: tetracycline, AAMS-biochar:
Alkali-acid (AA) binding method modified municipal sludge (MS)-biochar, data
represent the means ± standard errors of the means.
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